A pallet conveying apparatus for conveying one, two or more pallets, on which works are placed, in a circulating manner with respect to machine tools is known. A pallet conveying apparatus disclosed in JP2011-93032A includes a back pallet rail and a front pallet rail extending parallel to each other and pallet moving means for moving a pallet from the back pallet rail to the front pallet rail or from the front pallet rail to the back pallet rail by moving between two positions facing both end parts of the back pallet rail and the front pallet rail. This pallet conveying apparatus can convey a plurality of pallets on a rectangular path.
A work placed on the pallet is processed by machine tools provided around the pallet conveying apparatus. To facilitate work processings by the machine tools, the work preferably passes near the machine tools. To that end, the pallet is so configured that the work is placed on one side of the pallet. Since the pallets are conveyed on the rectangular path in the pallet conveying apparatus disclosed in JP2011-93032A, if the machine tools are provided along the front pallet rail, other machine tools for processing the works placed on the pallets mounted on the back pallet rail have to be provided between the front pallet rail and the back pallet rail. In this case, since an interval between the front pallet rail and the back pallet rail increases, it is substantially impossible to provide the machine tools along the back pallet rail.
JP2016-117117A discloses a pallet conveying apparatus with two straight rails parallel to each other at a predetermined distance from each other and pallet moving means for guiding a plurality of pallets, on which works are placed, from an end part of either one of the straight rails to an end part of the other straight rail by moving the pallets along an arcuate path.
The pallet moving means in the pallet conveying apparatus disclosed in JP2016-117117A includes an elevating rotary plate rotatable about a vertical axis and vertically movable, one, two or more short rails provided around the elevating rotary plate, and an index unit for elevating and lowering the elevating rotary plate and rotating the elevated elevating rotary plate. The one, two or more short rails are configured such that the pallets are mountable thereon, and continuous with the straight rails with the elevating rotary plate lowered. The index unit elevates and lowers and rotates the elevating rotary plate at a first position where the short rails are continuous with one straight rail and a second position where the short rails are continuous with the other straight rail.
In the pallet conveying apparatus disclosed in JP2016-117117A, the pallets can be circulated on the track-like path. If the pallets are conveyed on the track-like path, one side of each pallet can be constantly caused to face outward. Thus, machine tools can be arranged outside the two straight rails and works placed on the pallets respectively mounted on the two straight rails can be processed.